1. Field of the Invention
The present invention relates to semiconductor structures, and in particular, to bonded semiconductor structures.
2. Description of Related Art
In the prior art, bonding two different semiconductor wafers together, with one of the materials being a semiconductor compound III–V material (such as a gallium arsenide (GaAs) wafer to a silicon wafer), has been accomplished by intermediate “glue” layers, such as spin-on glass or wax. Bonding of these wafers requires an elevated temperature, resulting in large stresses in between wafers upon return to room temperature due to a mismatch in the coefficient of thermal expansion. These stresses often result in the bonded pair of wafers breaking or delaminating at room temperature.
In a prior art plasma bonding device, which is essentially a reactive ion etcher device, a plasma has been used for surface activation, i.e., activation of a semiconductor surface to be amenable to bonding. This direct wafer bonding using plasma surface activation is an alternative to using bonding agents (e.g., glue layer) for bonding silicon and other semiconductor materials. With respect to semiconductor compound III–V materials, such plasma bonding to silicon has been claimed for indium phosphide (InP) and gallium arsenide (GaAs) when a hydrogen, argon with hydrogen or H/He plasma is used.
The plasma may be created in a low-pressure gas by inducing an electron flow that ionizes individual gas molecules through electron-gas molecule collisions. Typically, electrons are accelerated in an electric field between two plate electrodes coupled to a radio frequency (RF) power source. The plasma is generated adjacent to the substrate wafer(s), with the wafers typically being co-planar with the electrode plates and supported by a substrate support member within the bonding chamber. The chemical species in the plasma are determined by the source gas or gases used, which include oxygen. Plasma surface activation increases the kinetics of the oxide reaction due to increased mobility of the ionic species created on the surfaces.